Field of the Invention
The present invention relates to a method for evaluating vitality of a plant, and a measurement system and an evaluation system that are used in this method.
Related Background Art
Evaluation of growth states of agricultural plants, such as trees, shrubs, horticultural plants, vegetables, etc., for early determination of an anomaly, such as a pathological change, senescence, or withering, etc., or production of agricultural products of high added value (such as, tomatoes with high sugar content) by cultivation by loading of a suitable degree of stress is becoming an important theme for environmental conservation, agriculture, agricultural product processing industry, etc.
As a conventional method of evaluating the growth states of such plants, a subjective method of visual observation, etc., based on experience is generally used. However, realization of a method of evaluation of growth states based on objective indices is desired.
For example, in Patent Literature 1 is described a method for measuring stress received by a plant by irradiating light on a green leaf of the plant and capturing the reflected light or transmitted light from the green leaf to make multiple measurements with time of spectral ratio characteristics of spectral ratios obtained by dividing spectral luminances of respective wavelengths of the reflected light or transmitted light by spectral luminances of the same wavelengths of reflected light or transmitted light from an object serving as a reference for the irradiated light, detecting, for the respective spectral ratio characteristics, a change wavelength range in which the spectral ratio changes greatly from a low spectral ratio in a red visible light range to a high spectral ratio in a near-infrared range, determining the variation with time of the change wavelength range, and evaluating that the stress received by the plant is greater when the transition toward the short wavelength side in the variation of the change wavelength range is greater.
Also, in Patent Literature 2 is described a method for evaluating environmental stress tolerability of a plant that includes evaluation of photostress tolerance of the plant by intermittently irradiating a photosynthetic organ of the plant with saturation light pulses under the absence of photosynthesis light to measure the level of photoinhibition of photosynthesis caused thereby.
Further, in Non-Patent Literature 1 and Non-Patent Literature 2 is described an observation of how a pattern of a delayed luminescence curve of a leaf changes according to difference in stress state of a tree, and it is described that a control group and a drought stress group can be identified by plotting a second corrected delayed luminescence amount, obtained by correction by chlorophyll amount per predetermined leaf area of a second delayed luminescence amount, which is a delayed luminescence amount corresponding to a time domain in which the delayed luminescence amount decreases when xylem pressure potential is decreased, against a first corrected delayed luminescence amount, obtained by correction by the chlorophyll amount per predetermined leaf area of a first delayed luminescence amount, which is a delayed luminescence amount corresponding to a time domain in which the delayed luminescence amount increases when the xylem pressure potential is decreased.